“What has happened to Murray after winning Wimbledon is a combination of many things,” Moya wrote. “Becoming the first British champion in London 77 years after Fred Perry was a milestone. He must have felt a little empty after chasing it and having the entire nation behind him. He relaxed. I imagine it took him a little while to get his rhythm back, and have the same motivation as before. I'm not saying that he can’t get it back in the future because we are talking about a great player who just won his second Grand Slam tournament and is sure to win more, but right now it’s not easy.”

Moya also criticized Murray's coach, Ivan Lendl. Moya believes Lendl is having Murray focus too much on the majors and not enough on the other tournaments. After winning Wimbledon, Murray lost in the round-of-16 in Montreal and in the quarterfinals of Cincinnati. Defending a major title for the first time, Murray fell to Stanislas Wawrinka in the U.S. Open quarterfinals earlier this month.

“The best way to arrive at a Grand Slam is winning a Masters 1000, winning matches and acquiring the confidence those victories gave you,” Moya wrote. “It is essential for tennis today. Lendl is focusing too much on him only being a player at the Grand Slams.”

The Spaniard says it is impossible to be No. 1 if a player only focuses on winning Grand Slam titles.

“It is something only do [Novak] Djokovic and [Rafael] Nadal can do. For me, Murray is neither Novak nor Rafa," Moya writes. "He can become one [of those types of players], but right now he is not. In terms of consistency, he is far away. Rafa has made 12 finals in 13 tournaments and has won 10. Djokovic has lost very few matches. Murray—not just this year—is a player who has trouble mentally enduring throughout the year.”

Murray recently pulled out of the Asian swing to undergo back surgery.